1. Field of the Invention
The present invention relates to semiconductor wafers having an epitaxially grown gallium arsenide layer, useful for fabricating various GaAs compound semiconducting devices, and methods suitable for producing such semiconductor wafers and devices.
2. Discussion of the Related Art
Group III-V compound semiconductors with a gallium arsenide (GaAs) layer have high carrier mobility, direct-gap band structure, and variable nature of band gap and lattice parameter or constant in the case of the compounds consisting of three or four elements. Owing to these characteristics, the Group III-V compound semiconductors have been enjoying expanding industrial applications for fabricating not only a variety of semiconductor elements such as high-speed transistors, laser diodes, light emitting diodes (LED), phototransistors, photodiodes and solar cells, but also integrated circuits incorporating these semiconductor elements. An active layer providing such an active element is formed in a monocrystalline substrate of gallium arsenide, by preferential diffusion or ion implantation technique, or alternatively as an epitaxial GaAs layer formed by epitaxy on the GaAs substrate crystal.
However, a monocrystalline gallium arsenide (GaAs) substrate suffers from some disadvantages over a monocrystalline silicon (Si) substrate, e.g., more difficulty in obtaining an ingot of a relatively large diameter, higher cost of production, and lower mechanical strength. In the light of these disadvatages of the monocrystalline gallium arsenide substrate, there has been an attempt to use a monocrystalline substrate of silicon, since the technologies for producing and processing its ingot are most advanced in the field of semiconductor materials. In this case, an active layer of gallium arsenide is epitaxially grown or formed by epitaxy on the surface of the nonocrystalline silicon substrate. However, the thus .obtained semiconductor wafer tends to have a lattice mismatch or dislocation of the epitaxial gallium arsenide active layer and the silicon substrate, and is not satisfactory in crystallinity of the active layer.